PROJECT SUMMARY Exposure to early life adversity (ELA) during critical periods of prenatal and postnatal development is an important risk factor for the later life onset of highly prevalent gastrointestinal (GI) diseases, including irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD). The precise mechanisms linking ELA and GI disease susceptibility are unknown and thus management and therapeutic targets and biomarkers are lacking. Our studies using a porcine model demonstrated that ELA alters the normal course of GI development resulting in lifelong intestinal barrier dysfunction or ?leaky gut', neuroimmune dysregulation and increased GI disease that recapitulates much of the pathophysiology and clinical features of human stress-related GI disorders. We recently identified two factors associated with ELA-induced GI disease susceptibility and severity in adulthood: (1) heightened and persistent intestinal mast cell hyper-activity and (2) biological sex with females at increased risk and males protected. Furthermore, we have identified novel sex-differences in the mast cell phenotype in that mast cell from female animals exhibit enhanced synthesis storage and stress-induced release of mediators such as histamine, proteases and serotonin which have known roles in GI neuroimmune disorders. Our hypothesis is that mast cells and biological sex interact to organize the development of GI barrier and neuroimmune systems, consequently determining the lifetime risk to disease following exposure to ELA. We have designed three specific aims to accomplish this objective. Aim 1 will test the hypothesis that hyper-activation of GI mast cells during early postnatal development lead to GI barrier and neuroimmune dysfunction in adulthood. Aim 2 will test the hypothesis that the heightened vulnerability of females to ELA-induced GI disease depends on androgens acting during early development. Aim 3 will test the hypothesis that ELA and perinatal androgens program mast cells, via epigenetic and transcriptional mechanisms, resulting in mast cell hyperactivity which drives GI barrier and neuroimmune dysfunction into adulthood. Together, the studies proposed in the grant application are expected to result in a major paradigm shift in the understanding the origins of ELA-induced and sex-biased GI neuroimmune diseases which could ultimately unveil new therapeutic targets to protect the GI system during vulnerable periods of stress and to therapeutically modulate adult diseases in both sexes.